Flip label separators to fix previous

-gpiokeys0 at mainbus0, "PWR Button"
+gpiokeys0 at mainbus0: "PWR Button"

OK patrick

The gpiokeys(4) 'label' property seems to be optional. If we don't have
any, don't try and print it, and especially don't error out.

Tested on Lenovo x13s (myself) and Pinebook Poop (kn@)
ok kn@

Add gpiokeys(4) for arm64

This driver handles events triggered by GPIO keys such as lid status and
power button.

OK kettenis